1. Technical Field
The invention relates to a detector, a physical quantity measuring device, and an electronic apparatus.
2. Related Art
A sensor circuit which measures a physical quantity, such as angular velocity, has been mounted in a vehicle, an electronic apparatus, and the like in order to detect vibration caused by vehicle movement, hand shaking, and the like. In recent years, as the sensor circuit is used for increasingly varied applications, there is a case where a plurality of outputs is output from a sensor circuit and the physical quantity is measured using each output according to their purposes, for example.
Various sensor circuits which output a plurality of outputs have been proposed. For example, JP-A-2000-88578 discloses an angular velocity sensor that includes two detection means, which detects detection signals with different polarities, and that detects a sensitivity change caused by failure and deterioration by monitoring the detection signals to thereby improve reliability. In addition, JP-A-2006-292469 discloses a capacitance-type physical quantity sensor that includes a first GAIN circuit and a second GAIN circuit, which amplifies the output of the first GAIN circuit and can change the gain at the time of detection of the acceleration and self-diagnosis, and that can perform self-diagnosis of both the output of the first GAIN circuit and the output of the second GAIN circuit simultaneously. In addition, JP-A-2002-267452 discloses a vibration detector that includes a first amplifying means and a second amplifying means with different gains and eliminates the offset of the first amplifying means by the output of the second amplifying means. In addition, JP-A-11-282502 discloses a digital feedback controller that changes the gain according to the amplitude of the output of a sensor so that the resolution of an A/D conversion means is substantially changed. In addition, JP-A-7-218270 discloses a vehicle movement detector which amplifies signals of two piezoelectric elements for detection using a switched capacitor circuit and in which the capacitance ratio of a capacitor, which is connected between the virtual ground end and the output end of an operational amplifier, and an input capacitor is variable. In addition, a second-order switched capacitor filter which is formed by a switched capacitor circuit and suppresses the spread of element values is disclosed in “Second-order SCF which suppresses the spread of element values” by Ishikawa, Anzai, Fujii, the Institute of Electronics, Information and Communication Engineers of Japan, Technical Report CAS89-163//CS89-123//DSP89-62.
Depending on the purpose of a sensor circuit, a wide detection range and high sensitivity need to be compatible. In this case, how to increase the sensitivity on one side by branching of one output of a sensor circuit is considered. In general, however, it is necessary to add a circuit. In this case, since noise increases, it is not possible to improve the S/N ratio. Therefore, it is desirable to change the detection range (dynamic range) of a sensor circuit at a low cost, for example, by outputting two outputs with different sensitivities from the sensor circuit without providing an external circuit.
Moreover, when the output load characteristics of a plurality of outputs with different sensitivities are different, it is necessary to provide a circuit (for example, an A/D converter) corresponding to the output load characteristic for every output from the sensor circuit. In this case, there is a problem that the costs increase in order to maintain the detection accuracy. Therefore, it is desirable to make the output load characteristics equal for every output from the sensor circuit.
In the devices disclosed in JP-A-2000-88578, JP-A-2006-292469, JP-A-2002-267452, and JP-A-11-282502, however, the power consumption increases even if the gain is simply changed, because the signal is amplified using a resistance element instead of a switched capacitor circuit. Moreover, in the device disclosed in JP-A-7-218270, the gain may be adjusted, but only sample and hold of a detection signal is performed. Accordingly, in the devices disclosed in JP-A-2000-88578, JP-A-2006-292469, JP-A-2002-267452, JP-A-11-282502, and JP-A-7-218270, noise is amplified as is. As a result, it is not possible to obtain a high-sensitivity output because noise is also amplified, even though the high-sensitivity output is needed. Moreover, in the devices disclosed in JP-A-2000-88578, JP-A-2006-292469, JP-A-2002-267452, JP-A-11-282502, and JP-A-7-218270, an offset voltage difference between operational amplifiers which amplify each output occurs. For example, both outputs are different even in a stopped state. As a result, there is a problem in that signal processing at the subsequent stage becomes complicated and the usability becomes worse accordingly. In addition, in the devices disclosed in JP-A-2000-88578, JP-A-2006-292469, JP-A-2002-267452, JP-A-11-282502, and JP-A-7-218270, it is not possible to make the output load capacity equal for every output when outputting a plurality of kinds of outputs.